Amazon considered different situations that may happen and reasons for a return. Who pays for the return shipping is determined by the reason for a return. In some cases, the buyer covers the cost; in other cases, it is paid by the seller. The policies also vary in each country, so if you sell internationally, you need to be familiar with the policies of each marketplace.
In general, returns due to the seller’s fault are paid by the seller. This includes return reasons such as defective items or missing parts. Returns due to the buyer’s fault (i.e., the item is no longer needed or wanted) are paid by the buyer.
For details, please visit Amazon Seller Central Help: